It is known that certain hydraulic conduits used in the automobile industry, and in particular those forming part of power steering systems, are provided with noise attenuators, often referred to in the art as “tuners”.
In general, a power steering system comprises in particular a high pressure circuit with a hydraulic pump that feeds fluid under pressure to a servo-valve which is connected to the rack device of the system for steering the steerable wheels of the vehicle. The hydraulic conduit which connects the pump to the servo-valve is made up of flexible segments constituted by pieces of hose and rigid segments constituted by tubes, and often at least one noise attenuator in the form of a flexible sheath of metal or plastics material which is mounted inside a flexible segment of the conduit in order specifically to attenuate the operating noise of the pump which tends to travel up the steering column into the vehicle cabin.
A first generation of power steering systems in which the hydraulic pump was driven by the engine shaft of the motor vehicle has now been replaced by a second generation in which the hydraulic pump is driven by an electric motor, with such power systems often being referred to in the art as being of the electrically-driven pump type.
With this second generation of power steering systems where the hydraulic pump is dissociated from the engine shaft of the vehicle, it is possible to locate the pump in any location, however the available space is usually close to the vehicle cabin, given the lack of space that remains available in the engine compartment which is already very full.
At present, there is a third generation of power steering systems which are of the electrically-powered pump type as mentioned above, but which are also pilot-controlled in the sense that the electric motor driving the hydraulic pump is put into operation only when the steering wheel is turned by the driver.
With this third generation of power steering systems of the pilot-controlled type, noise attenuators need to operate over a larger frequency range of about 150 Hz to 800 Hz.